1. Field of the Invention
The present invention relates to a novel oligohexafluoropropylene oxide derivative useful for the synthesis of fluororesins, fluororubbers, fluorine-containing surfactants, etc. and a process of producing the same.
2. Description of the Prior Art
An industrially applicable process of producing iodine-containing oligohexafluoropropylene oxides represented by the general formula (i): ##STR3## wherein R.sub.f represents a perfluoroalkyl group having 1 to 10 carbon atoms and n is an integer of 0 to 100 and the general formula (ii): ##STR4## wherein R.sub.f ' represents a perfluoroalkylene group having 2 to 10 carbon atoms and a and b are each independently an integer of 0 to 20 which are conventionally intermediates for synthesizing fluoroesins, fluororubbers, fluorine-containing surfactants, etc. is not known yet.
That is, hitherto, for example, to produce an iodine-containing oligohexafluoropropylene oxide of the general formula (i), a process is known wherein first, as is shown below, an oligohexafluoropropylene oxide carboxylic acid fluoride represented by the general formula (iii) used as a raw material is hydrolyzed to obtain a carboxylic acid (iv), then the carboxylic acid (iv) is converted to the silver salt (v) using silver oxide, and the silver salt (v) is thermally decomposed in the presence of I.sub.2 to obtain the iodine-containing oligohexafluoropropylene oxide of the general formula (i) (Japanese Pre-examination Patent Publication (kokai) No. 63-30441 (1988): ##STR5##
However, according to the above process, the yield of the intended iodine-containing oligohexafluoropropylene oxide (i) is about 70 to 85%. Further, in most of the cases, the silver salt that is an intermediate is solid, which means that the handling is difficult, and in addition there is a defect that since expensive silver is used, recovery of the silver is necessary where the process is industrially employed. Further, where the process is performed industrially, many problems are involved, for example, the process includes 3 steps, hydrogen fluoride which is toxic is given off during the process, and a thermal decomposition reaction is necessary for obtaining the intended product. There are also such disadvantages that, in view of the cost, expensive raw materials are used and the cost of facilities increases.
Therefore, it is demanded to produce an iodine-containing oligohexafluoropropylene oxide of the general formula (i) industrially advantageously without such problems.